Thermal, Optical, and Film Properties of a Ladder-like Polysilsesquioxane as Flexible Electronic Device Substrates
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Thermal, Optical, and Film Properties of a Ladder-like Polysilsesquioxane as Flexible Electronic Device Substrates Albert S. Lee1,2, Seung-Sock Choi1, He Seung Lee1, Hyeon Yeol Jeon1,2, Kyung-Youl Baek1,2, Seung Sang Hwang*1,2 1
Center for Materials Architecturing, Korea Institute of Science and Technology, Hwarangno 14gil 5, Seong-Buk Gu, Seoul 136-791 2
Nanomaterials Science and Engineering, University of Science and Technology, 217 Gajungro, 176 Gajung-dong, Yuseong-Gu, Daejeon, Korea 305-333 ABSTRACT A high molecular weight, photocurable inorganic-organic hybrid based on ladder-like poly(phenyl6-co-methacrylate4)silsesquioxanes (LPPMA64) was investigated as a flexible display substrate. Photocured free standing films with 40μm thickness showed high transparency (>95%), excellent thermal stability (Td >450°C), and low coefficient of thermal expansion (38ppm/K) without the use of reinforced glass fibers. Furthermore, these ladder-like structured materials did not require any thermal treatment processes due to the negligible amounts of uncondensed groups, thus simplifying manufacturing processing. These novel hybrid films present an alternative to organic plastics as flexible electronic device substrates due to their excellent optical and thermal properties. INTRODUCTION Over the past decade, extensive research has been conducted on the fabrication of flexible devices that offer advantages in being lightweight, bendable, conformable, and not easily breakable1. These flexible electronics encompass a broad class of research fields of which include many applications such as organic photovoltaics, organic light emitting diodes, flexible displays, and organic thin-film transistors2. As extensive research on flexible devices has been ongoing, the search for flexible substrates to supplant conventional glass substrates has been equally rigorous. Several studies have detailed the potential of organic plastics as an alternative to glass substrates1,2, which offer many advantages in transparency, light weight, flexibility, mechanical robustness, and easy manufacture in being able to processed by a roll-to-roll method. Commonly studied organic polymers include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonates (PC), polycyclic olefins (PCO), polyetheretherketone (PEEK), and polyimides (PI)1. However, many of the organic polymers mentioned above fail to meet in either one or several of the many specifications required of flexible display substrates1. Flexible display substrates not only require optical transparency, flexibility, and light weight, but also require excellent chemical and thermal stability, dimensional stability, high refractive index, low birefringence, and a low coefficient of thermal expansion(CTE)1,2, much like the properties of glass.
Polysilsesquioxanes are a class of inorganic-organic hybrid materials with chemical formula, [SiO1.5R]n3. These materials have silicon to oxygen ratios in between that of conventional SiO2 glass substrates and silicon oil R2SiO, thus retaining
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